1. Field of the Invention
This invention relates to a four-cycle engine, and more particularly to a four-cycle engine configured as a V-shape that has a suitable configured for an outboard motor.
2. Description of Related Art
Some outboard motors have recently employed a four-cycle engine in order to address environmental concerns. If an outboard motor is required to have a high power output, a multi-cylinder, V-shape engine is a typical selection for this purpose. For example, a V6, four-cycle engine is one engine type that can meet both of the foregoing demands, i.e., low emissions and high performance.
Because of its V shape, this type of engine typically includes an air induction system having a pair of air intake passages that supply air to combustion chambers in both of the cylinder banks. The air induction system also usually has a single or a pair of plenum chambers from which the air intake passages extend. The plenum chamber functions as an air silencer and/or an air coordinator for smoothing air flow to the respective combustion chambers.
In addition to high-speed performance, a typical outboard motor engine is required to operate at a trolling speed so that an associated watercraft can go forward very slowly. The trolling speed is obtained when the engine operates nearly at an idle speed. Generally, the longer the intake passages are, the better the engine will run at low engine speeds, i.e., at idle and trolling speeds. A single plenum chamber also is preferred over than multiple plenum chambers in order to lengthen the induction path to the engine cylinders.
A disadvantage arises, however, if the engine employs just one plenum chamber. A single plenum chamber must have openings on both its port and starboard sides that communicate with respective air intake passages. These air intake passages lead to the combustion chambers in the port and starboard cylinder banks, respectively. Normally, the plenum chamber and the intake passages are formed with members made of plastic or metal castings. Because of this, accurate positioning of an opening and a respective passage, which are mated together, can be difficult. This task is exacerbated by the fact that this step must be done with multiple passage and opening pairings and on both sides of the plenum chamber. Alignment on one side may throw-off alignment on the other side. This difficulty exists not only when the engine is assembled at a factory but also when the plenum chamber or the intake passages are replaced or removed during engine repair or maintenance.
A need therefore exists for an improved four-cycle engine having cylinders arranged in a V-shape configuration that is provided with an air induction system that is suitable for a low speed operation and that can be easily assembled and disassembled.
In accordance with one aspect of the present invention, a four-cycle, internal combustion engine comprises a cylinder body defining a plurality of cylinder bores. The cylinder bores extend generally horizontally and are spaced apart horizontally from each other to form a V-configuration. Pistons reciprocate within the respective cylinder bores. A pair of cylinder head members closes one ends of the cylinder bores to define combustion chambers with the cylinder bores and the pistons. A crankshaft is coupled with the pistons for rotation with the reciprocal movement of the pistons. A crankcase member closes another end of the cylinder bores to define a crankcase chamber in which the crankshaft extends generally vertically. An air induction system is arranged to introduce air into the combustion chambers. The air induction system includes a pair of plenum chamber members generally disposed on a side of the crankcase member opposite of the crankshaft. Both the plenum chamber members are positioned in close vicinity to each other. Each one of the plenum chamber members defines a plenum chamber to intake air into the air induction system. A balance pipe is affixed to both the plenum chamber members to couple together the plenum chambers.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment that follows.